1. Field of the Invention
This invention relates to a sheet feeding apparatus for a copying machine, printing machine, etc. which is provided with a sheet feeding tray for supporting sheets thereon capable of moving into and out of a main body of the machine and also in a vertical direction within the main body of the machine.
2. Description of the Prior Art
A sheet feeding tray of a sheet feeding apparatus for supporting sheets thereon is often moved out of a main body of a machine for replenishing the sheets or replacing the sheets by another set of sheets and then inserted into the machine. Upon reaching a predetermined position in the main body of the machine, the sheet feeding tray is lifted until the uppermost sheet of a stack of the sheets thereon comes into contact with a sheet feeding roller for performing a sheet feeding operation. The rotation of the sheet feeding roller feeds only the uppermost sheet to the destination through a pair of separation rollers. It has hitherto been customary to manually move the sheet feeding tray into and out of the main body of the machine, and to vertically move the sheet feeding tray by power within the main body of the machine. The result achieved by a manual operation of moving the sheet feeding tray into and out of the main body of the machine varies from operator to operator. Even if copy sheets are piled correctly in a stack on the sheet feeding tray, the stack of copy sheets will collapse when the sheet feeding tray is moved into the main body at an excessively high speed. When the sheet feeding tray is forcibly moved into the main body, there is a danger that trouble will occur in the machine.
In order that only the uppermost sheet is fed at one time from a stack of copy sheets on the sheet feeding tray, it is important that the uppermost sheet be maintained in a correct position at all times. To this end, a reduction in the number of copy sheets should be detected as soon as possible so as to raise the sheet feeding tray to correct the position of the uppermost sheet. In correcting the position of the uppermost sheet, the movement of the sheet feeding tray should not be effected abruptly to eliminate the influences of inertia and other factors. Stated differently, the sheet feeding tray should be moved quietly and slowly. On the other hand, in moving the sheet feeding tray into and out of the main body of the machine, problems may be raised with regard to the inertia which will be produced when a stack of sheets is suddenly stopped and with regard to the danger which will be experienced when the sheet feeding tray suddenly moves out of the main body of the machine. However, the movement of the sheet feeding tray into and out of the main body of the machine should be carried out as quickly as possible so long as these problems are not raised.